Process for the deposition of thin layers by chemical vapor deposition

ABSTRACT

A process for the deposition of thin layers by chemical vapor deposition includes adding an effective amount of nitroxyl radicals of the formula  
                 
 
     to a gas stream including the materials to be deposited. In this formula, R 1  and R 2  are identical or different alkyl, alkenyl, alkynyl, acyl, or aryl radicals, with or without heteroatoms. R 1  and R 2  can also together form a structure —CR 3 R 4 —CR 5 R 6 —CR 7 R 8 —CR 9 R 10 —CR 11 R 12 —, where R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , R 12  are again identical or different alkyl, alkenyl, alkynyl, acyl, or aryl radicals, with or without heteroatoms.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] The invention relates to a process for the deposition of thinlayers by chemical vapor deposition.

[0003] In the semiconductor industry, both physical vapor deposition(PVD) and chemical vapor deposition (CVD) processes are used for thedeposition of thin layers. Compared to PVD processes, the CVD processesgive better edge coverage and greater conformity throughout the coating.CVD processes are therefore used in particular for filling deep trenchcapacitors or contact holes. The films produced in this way can beeither dielectrics (e.g. silicon dioxide, silicon nitride, aluminumoxide, tantalum oxide, etc.) or metals and metal-containing compounds.In particular, layers of transition metals, e.g. tungsten, and oftransition metal silicides and nitrides, e.g. WN, WSix, CoSi, TaSi,etc., are deposited.

[0004] In CVD processes, the starting materials are introduced into thereactor chamber as gaseous compounds and react on the substrate surfaceto give the desired end product. The energy necessary for the reactionis introduced in the form of heat by heating the walls, radiation, orsusceptor/wafer heating. The typical temperature range for thedeposition is from 400° C. to 900° C.

[0005] However, there are applications, e.g. filling of structureshaving extreme aspect ratios or deposition on heat-sensitive layers suchas aluminum metalization or organic dielectrics, in which significantlylower temperatures, which are more than 100° C. below the abovementionedcustomary temperatures, are desirable. Lower temperatures increase edgecoverage and conformity and, secondly, the deposition of certain layerswithout damage to the underlying substrate is made possible for thefirst time.

[0006] Various disadvantages stand in the way of carrying out CVDprocesses at lower temperatures. Thus, for example, the deposition ofcertain layers can only be completed above a particular temperature, sothat reducing the temperature is not possible at all. In the case ofdepositions that can be completed in principle, the deposition rate issometimes reduced so much that the process cannot be completedeconomically. In other deposition reactions, only the nucleation step(i.e. the covering of the substrate surface with a first layer of thesubstance to be deposited) is problematical; further deposition canoccur at the reduced temperature.

[0007] For the reasons mentioned, attempts have been made to developmethods that enable CVD processes to be completed at relatively lowtemperatures. Such a method of reducing the temperature is thegeneration of plasma. The ions, free radicals, and excited moleculesformed in this way are more reactive than the starting molecules, sothat the deposition reactions can occur at lower temperature. However,these plasma enhanced chemical vapor deposition (PECVD) processesfrequently result, due to the reactivity and variety of substancesformed, in undesirable gas-phase reactions or undesirable secondaryreactions which then lead to increased contamination of the layers withextraneous substances.

[0008] U.S. Pat. No. 5,637,351 describes a method of increasing thedeposition rate in CVD processes. The method adds free-radical formersto the CVD reactor. The patent discloses using organic free-radicalformers in the deposition of SiO₂ from a diethylenesilane/oxygenmixture.

[0009] There nevertheless continues to be a need for processes thatenable the temperature in CVD processes to be decreased whilemaintaining economically justifiable deposition rates.

SUMMARY OF THE INVENTION

[0010] It is accordingly an object of the invention to provide a processfor the deposition of thin layers by chemical vapor deposition thatovercomes the hereinafore-mentioned disadvantages of theheretofore-known devices of this general type and that provides aprocess for the deposition of thin layers by chemical vapor deposition,which can be carried out at temperatures lower than those known from theprior art.

[0011] With the foregoing and other objects in view, there is provided,in accordance with the invention, a process for depositing thin layersby chemical vapor deposition. The first step is adding to a gas streamincluding materials to be deposited an effective amount of nitroxylradicals of the formula:

[0012] R₁ and R₂ are selected from the group including of alkyl,alkenyl, alkynyl, acyl, and aryl radicals. R₁ and R₂ can be identical ordifferent. The alkyl, alkenyl, alkynyl, acyl, and aryl radicals caninclude heteroatoms.

[0013] In accordance with a further object of the invention, the nextstep is forming from R₁ and R₂ a structure—CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—, wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉,R₁₀, R₁₁, R₁₂ can be identical or different and are selected from thegroup including alkyl, alkenyl, alkynyl, acyl, and aryl radicals with orwithout heteroatoms.

[0014] As stated, in the process of the invention for the deposition ofthin layers by chemical vapor deposition, an effective amount ofnitroxyl radicals of the formula

[0015] is added to the gas stream comprising the materials to bedeposited. In this formula, R₁ and R₂ are identical or it differentalkyl, alkenyl, alkynyl, acyl, or aryl radicals with or withoutheteroatoms. R₁ and R₂ can also together form a structure—CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—, where R₃, R₄, R₅, R₆, R₇, R₈, R₉,R₁₀, R₁₁, R₁₂ are again identical or different alkyl, alkenyl, alkynyl,acyl, or aryl radicals with or without heteroatoms.

[0016] In the process of the invention, nitroxyl radicals are added tothe gas mixture that is introduced into the reactor chamber. Thissignificantly reduces the deposition temperature compared toconventional CVD processes and the substrate is subjected toconsiderably less thermal stress. This is particularly advantageous whenheat-sensitive layers are already present, e.g. low-k dielectrics basedon organic compounds. In addition, a more conformal deposit is achieved.At a given reaction temperature, the addition of the nitroxyl radicalssignificantly increases the deposition rate or makes the reactionpossible for the first time. The nitroxyl radicals differ in theirreactivity, so that the deposition reaction can be controlled byappropriate selection of the substances. In addition, attachment of theradicals to the surface can increase the reactivity of the surface, thusallowing deposition on inert or passivated substrates.

[0017] Preference is given to embodiments in which R₁ and R₂ form astructure —CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—, in which R₃, R₄, R₅, R₆,R₇, R₈, R₉, R₁₀, R₁₁, R₁₂ are identical or different and are eachhydrogen, methyl or ethyl. Particular preference is given to R₁ and R₂forming a structure —CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂— in which R₃, R₄,R₁₁, R₁₂ are each methyl and R₅, R₆, R₇, R₈, R₉, R₁₀ are each hydrogen.The compound defined in this way, viz.2,2,6,6-tetramethyl-1-piperinyloxy, sublimes without decomposition underreduced pressure and is therefore very well suited to CVD applications.

[0018] The process of the invention is preferably employed for thedeposition of a dielectric material, in particular for the deposition ofsilicon dioxide, silicon nitride, aluminum oxide, tantalum oxide, or amixture thereof.

[0019] The process of the invention is also very well suited to thedeposition of a metal or a metal alloy, in particular for the depositionof tungsten, cobalt, tantalum, or a mixture thereof.

[0020] Good results are likewise obtained in the deposition ofmetal-containing compounds, in particular the deposition of a metalnitride or a metal silicide, with the deposition of WN, WSiX, CoSi,TaSi, or a mixture thereof being found to be very particularlyadvantageous.

[0021] The addition of free nitroxyl radicals is particularly usefulwhen only one precursor gas is utilized, i.e. when only one chemicalcompound apart from the added nitroxyl radicals is present in the gasstream including the materials to be deposited. The addition of nitroxylradicals greatly restricts undesirable secondary reactions or prematuregas-phase reactions.

[0022] As already explained, the addition of free nitroxyl radicalsserves to allow the CVD process to proceed at temperatures lower thanthose customarily employed. Preference is therefore given to carryingout the deposition at a temperature in the range from 100° C. to 500° C.The deposition is particularly preferably carried out at a temperaturein the range from 150° C. to 250° C.

[0023] In the process of the invention, preference is given to addingonly very small amounts of nitroxyl radicals to the gas mixture. If theprocess conditions or reaction mechanism are appropriate, very smallamounts of nitroxyl radicals can suffice. The nitroxyl radicals arepreferably added in a concentration of less than five percent (<5%),particularly preferably a concentration of less than one percent (<1%),to the gases required for the deposition.

[0024] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0025] Although the invention is illustrated and described herein asembodied in a process for the deposition of thin layers by chemicalvapor deposition, it is nevertheless not intended to be limited to thedetails shown, since various modifications and structural changes may bemade therein without departing from the spirit of the invention andwithin the scope and range of equivalents of the claims.

[0026] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In a preferred embodiment of the present invention, the nitroxylradicals are added to the gas mixture only at the beginning of thedeposition process. This procedure is particularly advantageous in CVDprocesses in which a nucleation step occurs first. In this case, it issufficient to add the radicals only during the initial period of time inorder to initiate the reaction. The actual deposition then continues asa free-radical chain reaction. An example of this embodiment of thepresent invention is the deposition of tungsten silicide. Nitroxylradicals are added during the nucleation step of the tungsten silicideCVD using a mixture of dichlorosilane and tungsten hexafluoride. Thedichlorosilane reaction proceeds via free radicals as intermediates, andthe nucleation step is temperature-critical. Once the nucleation layerhas been formed, the deposition continues without further addition ofnitroxyl radicals.

[0028] Particular preference is given to adding the nitroxyl radicalsfor a period of from 5 to 20 seconds at the beginning of the depositionprocess.

[0029] Preference is likewise given to an embodiment in which thenitroxyl radicals are alternately added to the gas mixture for aparticular time and then not added for a particular time during thedeposition process. This embodiment enables, for example, double ormultiple layers of different substances to be deposited. An example ofthis embodiment of the present invention is the deposition of a tungstenlayer or a WSi_(x) layer without addition of radicals, subsequentaddition of radicals and dichlorosilane to deposit silicon, andsubsequently renewed deposition of tungsten or tungsten silicide withoutaddition of radicals. This method achieves compoundcompositions/stoichiometries that are not possible by simultaneousdeposition. The length of the periods of time during which nitroxylradicals are added and not added depends on the thickness of the layerthat is to be deposited in each case.

[0030] Particular preference is given to continuous addition of thenitroxyl radicals to the gas mixture during the entire depositionprocess. In this way, a reduction in the temperature and/or accelerationof the deposition can be achieved. Examples of this embodiment of thepresent invention are the deposition of SiO₂ using SiH₄/O₃ or TEOS/O₂mixtures, the deposition of Si₃N₄ using NH₃/SiH₄ mixtures, thedeposition of metal silicides using dichlorosilane or silane and thedeposition of silicon using silane, disilane, and dichlorosilane.

[0031] The process of the invention can be employed particularlyadvantageously for the deposition of thin layers on semiconductormaterials, for filling deep trench capacitors and for filling contactholes.

EXAMPLES

[0032] The ranges given in brackets for pressure, temperature and gasflows in the examples below indicate the possible process window. Theindividual values can be varied within these ranges, and the layersdeposited then differ in terms of their composition (e.g. the tungstensilicide can be enriched with W or Si) and/or deposition rates. Thedeposition can thus be matched to the particular requirements.

Example 1

[0033] A batch process, i.e. one in which a plurality of wafers can becoated simultaneously, is conducted in a vertical furnace (for example,from SVG, model AVP 8000) having a capacity of up to 150 wafers.

[0034] A silicon nitride layer is deposited according to a CVD process.Ammonia (NH₃) and dichlorosilane (SiCl₂H₂) were used as precursor gasesin the presence of the radical 2,2,6,6-tetramethyl -1-piperidinyloxy.

[0035] The deposition is conducted in a temperature range from 400 to500° C. This range contrasts standard temperatures for the deposition ofsilicon nitride, which are from 650 to 800° C. Flow rates: ammonia 280sccm (230-400 sccm) dichlorosilane  70 sccm  (40-150 sccm) 2,2,6,6-  3sccm  (2.5-4 sccm) tetramethyl-1- piperidinyloxy total pressure 150 torr(100-250 torr)

Example 2

[0036] The deposition is conducted in a single wafer unit (model“Centura” from Applied Materials). The wafer is heated from below viathe support, and the gases are introduced above the wafer.

[0037] A tungsten silicide layer is deposited on a substrate in a CVDprocess. Precursor gases used are tungsten hexafluoride (WF₆) anddichlorosilane (SiCl₂H₂). The radical2,2,6,6-tetramethyl-1-piperidinyloxy is added during a nucleation stepthat precedes the actual deposition. The radical is added for a periodof 15 sec (from 7 to 25 sec).

[0038] The deposition is conducted in a temperature range from 300 to400° C. This range contrasts standard temperatures for the deposition oftungsten silicide, which are from 500 to 600° C. Flow rates: tungstenhexafluoride  3 sccm  (1-5 sccm) dichlorosilane 300 sccm (100-300 sccm)2,2,6,6-tetramethyl-1-  2.5 sccm  (1.5-3.5 sccm) piperidinyloxy totalpressure  1.0 torr  (0.7-5 torr)

Example 3

[0039] The deposition is conducted in a single wafer unit (model“Centura” from Applied Materials). The wafer is heated from below viathe support, and the gases are introduced above the wafer.

[0040] The layer sequence polysilicon/tungsten silicide/polysilicon isdeposited on a substrate according to a CVD process. Precursor gasesused are tungsten hexafluoride (WF₆) and dichlorosilane (SiCl₂H₂).2,2,6,6-tetramethyl-1-piperidinyloxy is used as radical.

[0041] The deposition is conducted in a temperature range from 300 to400° C. This range contrasts standard temperatures for the deposition oftungsten silicide, which are from 500 to 600° C., and for polysilicon,which is normally deposited at temperatures above 600° C.

[0042] The specific parameters for the deposition of the various layersare as follows:

[0043] a) silicon layer Flow rates: tungsten hexafluoride  0dichlorosilane 300 sccm (100-300 sccm) 2,2,6,6-tetramethyl-1-  2.0 sccm (1-4 sccm) piperidinyloxy total pressure  3.0 torr  (0.7-5 torr)

[0044] b) tungsten silicide layer Flow rates: tungsten hexafluoride  3sccm  (1-5 sccm) dichlorosilane 300 sccm (100-300 sccm)2,2,6,6-tetramethyl-1-  0 piperidinyloxy total pressure  1.0 torr (0.7-5 torr)

[0045] c) silicon layer Flow rates: tungsten hexafluoride  0dichlorosilane 300 sccm (100-300 sccm) 2,2,6,6-tetramethyl-1-  2.0 sccm (1-4 sccm) piperidinyloxy total pressure  3.0 torr  (0.7-5 torr)

I claim:
 1. A process for depositing thin layers by chemical vapordeposition, which comprises: adding to a gas stream including materialsto be deposited an effective amount of nitroxyl radicals of the formula

the R₁ and R₂ being selected from the group consisting of alkyl,alkenyl, alkynyl, acyl, and aryl radicals.
 2. The process according toclaim 1, wherein R₁ and R₂ are identical.
 3. The process according toclaim 1, wherein R₁ and R₂ are different.
 4. The process according toclaim 1, which further comprises including heteroatoms in the groupconsisting of alkyl, alkenyl, alkynyl, acyl, and aryl radicals.
 5. Theprocess according to claim 1, which further comprises not includingheteroatoms in the group consisting of alkyl, alkenyl, alkynyl, acyl,and aryl radicals.
 6. The process according to claim 1, which furthercomprises: forming from R₁ and R₂ a structure—CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—; wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉,R₁₀, R₁₁, R₁₂ are selected from the group consisting of alkyl, alkenyl,alkynyl, acyl, and aryl radicals.
 7. The process according to claim 6,wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂ are identical.
 8. Theprocess according to claim 6, wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀,R₁₁, R₁₂ are different.
 9. The process according to claim 6, whichfurther comprises including heteroatoms in the group consisting ofalkyl, alkenyl, alkynyl, acyl, and aryl radicals.
 10. The processaccording to claim 6, which further comprises not including heteroatomsin the group consisting of alkyl, alkenyl, alkynyl, acyl, and arylradicals.
 11. The process according to claim 1, which further comprisesforming from R₁ and R₂ a structure —CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—;wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂ are selected from thegroup consisting of hydrogen, methyl, and ethyl.
 12. The processaccording to claim 11, wherein R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂are identical.
 13. The process according to claim 11, wherein R₃, R₄,R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, are different.
 14. The processaccording to claim 1, which further comprises forming from R₁ and R₂ astructure —CR₃R₄—CR₅R₆—CR₇R₈—CR₉R₁₀—CR₁₁R₁₂—; wherein R₃, R₄, R₁₁, R₁₂are each methyl, and R₅, R₆, R₇, R₈, R₉, and R₁₀ are each hydrogen. 15.The process according to claim 1, wherein at least one of the materialsto be deposited is a dielectric.
 16. The process according to claim 15,wherein the dielectric to be deposited is selected from the groupconsisting of silicon dioxide, silicon nitride, aluminum oxide, tantalumoxide, and a mixture thereof.
 17. The process according to claim 1,wherein at least one of the materials to be deposited is a metal alloy.18. The process according to claim 17, wherein the metal alloy is amixture of metals selected from the group consisting of tungsten,cobalt, and tantalum.
 19. The process according to claim 1, wherein atleast one of the materials to be deposited is a metal.
 20. The processaccording to claim 18, wherein the metal is selected from the groupconsisting of tungsten, cobalt, and tantalum.
 21. The process accordingto claim 1, wherein at least one of the materials to be deposited is ametal-containing compound.
 22. The process according to claim 22,wherein said metal-containing compound is selected from the groupconsisting of a metal nitride and a metal silicide.
 23. The processaccording to claim 21, wherein said metal containing compound isselected from the group consisting of WN, WSi_(x), CoSi, TaSi, and amixture thereof.
 24. The process according to claim 1, wherein only onechemical compound apart from the added nitroxyl radicals is present inthe gas stream including the materials to be deposited.
 25. The processaccording to claim 1, which further comprises heating to a temperaturebetween 100° C. and 500° C.
 26. The process as claimed in claim 1, whichfurther comprises heating to a temperature between 150° C. and 250° C.27. The process according to claim 1, which further comprises adding thenitroxyl radicals to the gas mixture in a concentration of less thanfive percent (<5%).
 28. The process according to claim 27, which furthercomprises adding the nitroxyl radicals to the gas mixture in aconcentration of less than one percent (<1%).
 29. The process accordingto claim 1, which further comprises adding the nitroxyl radicals the gasmixture only at the beginning of the deposition process.
 30. The processaccording to claim 29, which further comprises adding the nitroxylradicals to the gas mixture only for a period from five to twentyseconds (5-20 sec.) at the beginning of the deposition process.
 31. Theprocess according to claim 1, which further comprises alternativelyadding the nitroxyl radicals to the gas mixture for a particular timeand then not adding the nitroxyl radicals for a particular time duringthe deposition process.
 32. The process according to claim 1, whichfurther comprises continuously adding the nitroxyl radicals to the gasmixture during the entire deposition process.